1. Field of the Invention
This invention relates to a geomagnetic azimuth angle sensor or direction sensor and a method for manufacturing the same. More particularly, it relates to a geomagnetic azimuth angle or direction sensor exploiting magneto-resistance effects, and a method for manufacturing the same. It is noted that, the term "direction" herein means a direction relative to the direction of geomagnetism, and the term "azimuth angle" herein means the angle between a direction and the direction of geomagnetism.
2. Background of the Invention
In a color cathode ray tube, for example, it is a frequent occurrence that the trajectory of an electron beam radiated from an electron gun is sent by geomagnetism, thus causing variations in the beam landing position on a phosphor surface. With a high definition cathode ray tube, such changes in the landing, that is, a position deviation, give rise to problems such as deterioration in color purity.
For correcting such changes in the beam landing position, a landing correction coil is usually mounted on the cathode ray tube. An optimum current necessary for landing correction is automatically caused to flow through the landing correction coil depending on the geomagnetic direction for controlling the electron beam trajectory for prohibiting mistaken landing.
Thus, for landing correction, it is necessary to detect the geomagnetic direction accurately. To this end, a geomagnetic direction sensor is employed.
The geomagnetic direction sensor is also employed as a portable goniometer in place of a conventional magnet type goniometer or magnetic compass.
The representative structure of the geomagnetic direction sensor, employed for a number of purposes, may be classified into a so-called flux gate type and a magneto-resistive type (MR type).
The flux gate type geomagnetic direction sensor is comprised of a coil for outputting electrical signals 102 and an excitation coil 103, both wound on a permalloy core 101, as shown in FIG. 1. The flux gate type geomagnetic direction sensor is of such a construction in which the earth's magnetism is collected by the permalloy core and transmitted to the coil for outputting the electrical signal 102.
With the flux gate type geomagnetic direction sensor, an ac bias magnetic field is generated by the excitation coil 103 in the permalloy coil 101 and a pulsed voltage generated on bias magnetic field inversion is detected as a signal. Since the pulsed voltage is changed in magnitude depending on the geomagnetic direction, the geomagnetic direction sensor may be utilized as a geomagnetic sensor.
However, since the flux gate type geomagnetic direction sensor converts the geomagnetism into electrical signals by the coil, it is necessary to increase the number of turns of the coil for outputting the electrical signals 102 for improving sensitivity, while it is necessary to enlarge the size of the permalloy core 101 for improving flux-converging effects. Thus, it is difficult to reduce the size of the flux gate type sensor or to reduce its production cost.
On the other hand, the MR type geomagnetic sensor is comprised of a MR sensor chip 110, having formed thereon magneto-resistive effect devices (MR devices) 111 and introduced into an air-core coil 112, is so arranged that an ac bias magnetic field H.sub.B in a 45.degree. direction with respect to the MR devices 111 is applied to the MR sensor chip 110, as shown in FIG. 2. There is shown in FIG. 3 an equivalent circuit of the MR type geomagnetic sensor. When the MR sensor is employed as the geomagnetic direction sensor, a pair of the MR sensors shown in FIG. 2 are mounted so that the winding directions of the air-core coils run at right angles to each other.
The MR type geomagnetic direction sensor, making use of the MR sensors, is higher in sensitivity than the flux gate type geomagnetic direction sensor. However, the MR type geomagnetic direction sensor is not satisfactory in sensing the geomagnetic direction on the order of 0.3 gauss since the geomagnetism is sensed solely by the MR sensor chip.
In addition, since the bias magnetic field H.sub.B in the 45.degree. direction is applied to the MR devices 110, and an MR characteristic curve is forcedly raised at an acute slope for improving sensitivity, the MR type geomagnetic direction sensor exhibits hysteresis in MR characteristics which has to be eliminated by a complicated signal processing circuit. The MR type sensor also has a defect that the direction sensing sensitivity is low and even amounts to .+-.10.degree..
As discussed above, the conventional geomagnetic direction sensor is unsatisfactory in sensitivity, while it is difficult to reduce its size or production cost.